The overall objective is to understand how a multipotent stem cell, the interstitial cell of hydra, becomes committed to a specific differentiation pathway. Information is sought on [1] the number of steps in the commitment process: [2] whether the pattern of restriction from the multipotent stem cell to a differentiated cell is through a defined set of cell lineages or a disorderly pattern of restrictions; [3] whether the control of commitment is internal to the stem cell or influenced by external factors; [4] a more complete description of the differentiation pathways of the interstitial cell system. The approach will be to follow the proliferation and differentiation behavior of individual interstitial cells for 1-10 generations, as well as for more generations for some questions. As part of this effort we will attempt to construct a transgenic hydra carrying the E. coli beta-galactosidase gene, which will serve as a means of marking the individual interstitial cell. As it is a prominent feature of the system, the basis of the position-dependent pattern of differentiation will be explored in three ways: [1] Selective migration of precursors for some differentiation products plays an important role. Whether it is important for the rest will be examined. [2] The role of the head, foot or developmental gradients as the basis of the selective migration will be examined. [3] The differentiated state of sone nerve cells is metastable with respect to type of nerve cell. Whether a similar metastable state exists for the gland cells and mucous cells will be explored.